1. Field of the Invention
The present invention relates to the radiation structure of a power module including a semiconductor integrated circuit.
2. Description of the Related Art
Semiconductor integrated circuits have been widely used in various fields including electric cars. Especially, a semiconductor integrated circuit containing a power transistor is used for a device requiring large power. Thus, since a power module including such a power transistor is accompanied by considerable heat, a radiation structure using a heat sink is normally adopted.
FIG. 1 shows the radiation structure of a power module. In FIG. 1, a silicon chip 1 contains a semiconductor integrated circuit, and includes, for example, a power transistor. The silicon chip 1 is attached to a molybdenum plate 3 with solder 2. The molybdenum plate 3 is attached to a radiation plate 5 with silver wax 4. The molybdenum plate 3 is inserted between the silicon chip 1 and the radiation plate 5 because the radiation plate 5 is normally formed by a copper plate whose thermal expansion rate is different from that of the radiation plate 5. That is, when the silicon chip 1 is attached to the radiation plate 5 with solder, the silicon chip 1 and the radiation plate 5 may have a crack due to the difference in thermal expansion rate.
The above mentioned radiation plate 5 is mounted in a heat sink 6 formed by aluminum, etc. The power module shown in FIG. 1 is a non-insulating module, and is attached through an insulating sheet 7 made of a silicon and rubber sheet, etc. The radiation plate 5 and the heat sink 6 are attached using screws not shown in FIG. 1.
However, the radiation structure of the above mentioned power module has the following problems. That is, the above mentioned radiation structure of the power module requires the molybdenum plate 3, and the attachment using solder and silver wax. Therefore, the number of required parts increases, and the number of steps in the assembly process also increases.
When a non-insulating power module is used, the insulating sheet 7 is required. The thermal conductivity of the insulating sheet 7 is normally low, and the entire thermal resistance becomes high even if a single power module has low thermal resistance.
To compensate for the low thermal conductivity of the insulating sheet 7 using the radiation plate 5 of copper (Cu), it is necessary to increase a heat capacity, that is, to have a larger radiation plate 5. However, a larger radiation plate 5 makes a larger and heavier power module.
The present invention aims at providing the radiation structure of a power module without a insulating sheet, but with a smaller radiation plate to make the power module smaller and lighter, and with a smaller number or steps in an assembly process.
That is, the present invention provides the radiation structure of a power module formed by a semiconductor chip and ceramics including a conductive unit containing metal. The conductive unit includes a radiation plate to which the semiconductor chip is attached with solder, and a heat sink attached to the ceramics portion of the radiation plate.
The semiconductor chip is provided with a power element such as a power transistor, etc., and emits large heat. The radiation plate is made of ceramics, that is, a material having high thermal conductivity. For example, it has a sintered structure of SiC (silicon carbide) or AlN (aluminum nitride) according to claim 3.
In addition, the radiation plate is made of ceramics as described above, and is an excellent radiating and insulating material. To the insulating material with the above mentioned configuration, for example, a metal solution is added to form a conductive unit to which the semiconductor chip is attached with solder to provide the insulating unit with a radiating heat sink.
With the configuration, the radiation plate can be connected as an electrode of a non-insulating power module while the heat sink as a radiating unit of a semiconductor chip can be connected to an insulating portion to efficiently transmit the heat of the semiconductor chip to the heat sink through the radiation plate, thereby performing an efficient radiating process.